1. Field of the Invention
The present invention relates to an improvement in a camera having a magnetic head which reproduces information written to a magnetic storage portion provided for the film during the conveyance of the film.
2. Related Background Art
Recently, a camera has been disclosed in U.S. Pat. No. 4,965,627 which uses a film which has a magnetic recording portion, in which photography information such as the shutter speed, the diaphragm value, the date and the title is written to the magnetic recording portion and the photography information is read out when it is required.
When the film is wound to the film winding spool of a camera, the diameter of the film winding spool is gradually enlarged. Therefore, the film feeding speed is accelerated. That is, the film feeding speed is different between the first frame and the final frame of the film.
When information is read out by a magnetic head at the time of feeding the film, the signal level detected by the magnetic head is in proportion to the film feeding speed. That is, the signal level detected by the magnetic head is low at the first frame because the film feeding speed is relatively low. The signal level detected by the magnetic head is gradually raised adjacent to the final frame because the film feeding speed is raised.
In order to prevent an influence of an external noise, there is a desire of the digital conversion level set for an A/D (analog-to-digital) converter disposed in a magnetically reproducing circuit to be higher than a level at the time of the non-operation of the magnetic head, that is the level at the normal state. However, since the film feeding speed is too low at the leading portions of the film roll as described above, the levels of the signals reproduced in this state are too low and thereby signals the levels of which do not reach the digital conversion level are undesirably generated. Therefore, there arises a problem in that an error takes place at the time of reading information.
If the digital conversion level is set to a lower and constant level than the level at the constant state, the influence of the external noise easily affects regardless of the film feeding speed. Therefore, the noise is undesirably digital-converted, causing a problem to arise in that a reproduction signal becomes different from the actual signal (write signal).
A camera of a type the feeding speed of which can be changed, that is the photographing mode of which can be switched over encounters the problem of the above-described type.
Furthermore, the change in the film feeding speed causes the frequency and the amplitude of the reproduction signal to be changed in accordance with it. Therefore, the S/N ratio (signal-to-noise ratio) of the reproducing device will be deteriorated. Therefore, the reproduction signal generated in this case suffers from undesirable reliability.